Synthesis and chemical sensing application of two

High-Performance Chemical Sensors Using Novel Two-Dimensional Materials
Liang Chen
Advisor: Prof. Chongwu Zhou
Motivation
Why Choosing 2D Materials?
Smog is one kind of
air pollution that is
highly harmful to
humans. It was
once a big problem
around Los Angeles
Advantages:
• Small dimension
• High surface-to-volume ratio
• Semiconducting
areas in the 1950s. And now Beijing! Scientists
has discovered that smog is mostly caused by
the emission of NOx gases from cars. In this
sense, an efficient gas sensor is desired to
monitor these toxic gases.
(a)
(c)
A. K. Geim, I. V. Grigorieva, Van der Waals heterostructures. Nature, 2013, 499, 419-425
(e)
(b)
(c)
0.27 nm
2 nm
E
19-21cm
A1g
WSe2
2g
360
380
400
420
19-21cm
E
A1g
2g
2 nm
80
0.5
40
380
400
420
Back-gated
Field Effect Transistors
Si
1.0
60
(a)
0.5
40
(c)
Raman shift (cm )
2.28
20
2.2
2.1
2.28
0
2.3
2.2
-1
Raman shift (cm )
2.0
1.9
1.8
1.7
Photon energy (eV)
5 μm
1 μm
1.9
1.8
1.7
(d)
40 V
30 V
20 V
10 V
0V
-10 V
-20 V
2.27
2.1
2.0
Photon
energy (eV)
50 V
2.5
2.0
20
2.27
5 mm
0
2.3
MoS2
(b)
MoS2
(c)
-1
Si
1.0
60
360
80
IDS (mA)
-1
Normalized PL Intensity (a.u.)
0.27 nm
(f)
532 nm
Intensity (a.u.)
(e)
-1
10 mm
10 mm
(d)
(f)
532 nm
Intensity (a.u.)
(b)
(a)
10 mm
Normalized PL Intensity (a.u.)
MoS2(d)
Chemical Vapor Deposition (CVD)
Sensing Devices
10 mm
1.5
1.0
0.5
1.6
VBG
0.0
0V
1V
2V
3V
4V
5V
0.8
0.4
0.0
0
10 mm
VDS
1.2
IDS (mA)
Optical, AFM, Raman
2D MoS2 and WSe2 Synthesis
(a)
(b)
Transitional Metal Dichalcogenides
(TMDCs):
• Semiconductor with tunable
bandgap
• Direct bandgap at monolayer
1
2
3
4
5
Schottky
Contacts
Before NO exposure
10
5
0.0
5
-20
0
VBG (V)
20
0
40
(d)
1
0
3003
400
4
DS
1 ppm
5 ppm
10 ppm
50 ppm
200 ppm
500 ppm
2 nm
In 500 ppm NH3
0.2
-20
0
VBG (V)
20
40
-60
360
1600
0.1
0
200
1
300
2
400
3
500
NH3 concentration
(ppm)
V (V)
60
4
DS
Subthreshold voltage shifts upon gas
exposure
5
90
40
20
120
0
Before
1 ppm
5 ppm
10 ppm
50 ppm
200 ppm
500 ppm
50
380
DS
0.3
100
200
300
400
0
60
40
20
40
60
400
0
0
1000
10
30
60
90
120
Time (min)
3
4
420
0.1
Si
0.0
5
0
VDS (V)
0.5
MoS2
VBG = 0V
2Vacuum
3
4
1
ec
e φAu
2.28
20
0
2.3
(b)
2.2
SB1
SB2
2.1
SB
5
VDS (V)
EC
EF
2.27
Au
500
-1100
NH3
2
40
In 500 ppm NH3
0.2
Eg
Raman shift (cm )
800
0
1
1.0 (a)
VBG =30 V
NO2 concentration (ppb)
(d)
(f)
400
80
0.0
20
Before NH3 exposure
IDS (mA)
In 400 ppb NO2
Mechanism
100
80
Time (min)
1200
0 0.0 100
30
100
-10
NH3
Before
20 ppb
40 ppb
100 ppb
200 ppb
400 ppb
-40
2000
10
0
-20
(c)
(d)
Before NH3 exposure
20
(b)
(e)
(f)
60
-80 NO2
0
5
30
VDS=5V
-40
1 200 2
(b) 0.3
Vth(V)
IDS (mA)
2
0100
NO2 concentration
(ppb)
V (V)
4 Before exposure
3
0.0
IDS (mA)
(b)
0.3
2g
0
G/G0 (%)
0.27 nm
15
NO2
-40
In 400 ppb NO2
0.6
G/G0 (%)
0.1
IDS (mA)
0.2
Before exposure
20 ppb
40 ppb
100 ppb
200 ppb
400 ppb
(a)
(c)
Before NO2 exposure
20
Vth (V)
IDS (mA)
0.3
VDS=5V
25(a) 0.9
G/G0 (%)
(c)
G/G0 (%)
NO2 and
(a)
0.4
532 nm
NH3 Sensingand
Sensing
19-21cm-1
A1g
E
I (mA)
Normalized PL Intensity (a.u.)
(e)
Intensity (a.u.)
(d)
0
10 mm
(f) 0.3
2
0.6
-20
VBG (V)
VDS (V)
(e) 0.9
-40
EV
MoS2
NO2d-
2.0
1.9
NH3d’+
E1.8
C
Photon energyE (eV)
EF
g
EV
0
100
200
300
400
500
NH3 concentration (ppm)
Real time sensing results
Au
MoS2
Schottky barrier modulation
after gas absorption
Conclusion
We have successfully synthesized two-dimensional atomic layers of TMDC materials using CVD method, which facilitates the future
large scale fabrication of high density gas sensing arrays. High performance NO 2 and NH3 gas sensors using Schottky contacted 2D
materials were demonstrated. Results show that the detection limits can be down to 20 ppb for NO2 and 1 ppm for NH3, which are
superior to most of the other gas sensors.
1. Bilu Liu,† Liang Chen,† Gang Liu, Ahmad N. Abbas, Mohammad Fathi, and Chongwu Zhou*, High-Performance Chemical Sensing Using Schottky-Contacted Chemical Vapor
Deposition Grown Monolayer MoS2 Transistors. ACS Nano, 2014, 5, 5304-5314.
2. Liang Chen, † Bilu Liu, † Ahmad N. Abbas, Yuqiang Ma, Xin Fang, Yihang Liu, Chongwu Zhou*, Screw-Dislocation-Driven Growth of Two-Dimensional Few-Layer and
Pyramid-like WSe2 by Sulfur-Assisted Chemical Vapor Deposition. ACS Nano, 2014, Accepted.
[email protected]
Nanolab.usc.edu
1.7

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